Banca de DEFESA: LUCAS SANTOS HONDA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : LUCAS SANTOS HONDA
DATE: 31/07/2025
TIME: 09:00
LOCAL: Departamento de Agrotecnologias e Sustentabilidade
TITLE:

Humic substances in soils of Central Amazonia: effect of relief and vegetation on carbon stabilization

KEY WORDS:

infrared spectroscopy, humic acid, fulvic acid, humin, carbon persistence

PAGES: 50
BIG AREA: Ciências Agrárias
AREA: Agronomia
SUBÁREA: Ciência do Solo
SPECIALTY: Manejo e Conservação do Solo
SUMMARY:

A decade after the Paris Agreement (COP21, 2015), global efforts to limit the increase in the planet's average temperature to 1.5°C by 2030 have proven insufficient. More recent scientific projections indicate that this limit will most likely be exceeded this decade, and may be exceeded up to three years earlier than initially established. In this scenario, the Amazon biome assumes a central role in discussions on climate change and greenhouse gas (GHG) mitigation strategies. The Amazon acts as one of the largest carbon sinks on the planet, with an estimated annual sequestration of between 421 and 470 Tg of carbon (C), in addition to playing essential roles in climate regulation on a regional and global scale. Understanding the mechanisms that control the dynamics and stabilization of organic matter in Amazonian soils is therefore fundamental for both the conservation of ecosystem services and the development of effective strategies to mitigate GHG emissions. In this context, this study aimed to quantify carbon stocks (ECOS) in soil humic fractions (fulvic acid, humic acid, and humin) down to 30 and 100 cm depths, as well as to evaluate the influence of edaphic factors such as relief, drainage, and vegetation on the formation and stabilization of soil organic matter (SOM) in soils of the Urucu Province, Central Amazon. In 2018, trenches were dug and soil samples (disturbed and undisturbed) were collected from 10 representative profiles. The previously identified samples were packaged in plastic bags and sent to the Soil Organic Matter Dynamics Laboratory (LMOS), where they were prepared as air-dried fine earth (AFFI). To evaluate ECOS and carbon stabilization mechanisms, chemical fractionation of organic matter was performed, aiming at the separation of fulvic acid (FA), humic acid (HA) and humin (H) fractions, according to the methodology proposed by Benites et al. (2003). The quantification of organic carbon in the fractions was performed based on oxidation by potassium dichromate and titration with ammonium ferrous sulfate, according to Yeomans & Bremner (1988). Using the carbon contents obtained, ECOS were calculated at depths of 0–30 cm and 0–100 cm. ECOS at 30 cm ranged from 16.4 to 67.5 Mg ha⁻¹, while ECOS at 100 cm ranged from 51.5 to 214.2 Mg ha⁻¹. In the fulvic fraction, soils on dry land, well-drained and under dense forest presented stocks between 23.1 and 51.8 Mg ha⁻¹; in the humic fraction, between 8.4 and 33.1 Mg ha⁻¹; and in humin, between 24.1 and 68.0 Mg ha⁻¹. In profiles located in river plains, with impeded drainage and open forest vegetation, ECOS varied between 19.2 and 63.1 Mg ha⁻¹ (AF), 22.3 and 79.0 Mg ha⁻¹ (AH), and between 28.1 and 72.1 Mg ha⁻¹ (H). In soils located on terraces, with moderate to imperfect drainage and under open forest, stocks ranged from 16.0 to 46.7 Mg ha⁻¹ (AF), 7.7 to 54.3 Mg ha⁻¹ (AH), and 22.5 to 98.8 Mg ha⁻¹ (H). Only two profiles presented more than 50% of the total carbon stock in the top 30 cm, notably a Gleysol, which concentrated 64.7% of the organic carbon in this surface layer. The results indicate a strong influence of soil conditions and the environment on the vertical distribution and stability of carbon in the different humic fractions of the soil.

COMMITTEE MEMBERS:
Presidente - 1740899 - ERIKA FLAVIA MACHADO PINHEIRO
Externa ao Programa - 3421788 - RENATA COURA BORGES - UFRRJExterno à Instituição - DAVID VILAS BOAS DE CAMPOS - EMBRAPA